Touch sensitive keypad

[Viacheslav] built a keypad that uses human capacitance to detect key presses. Unlike normal keys which close a physical connection, his project detects touch through the PCB substrate. He uses the analog comparator of an AVR ATmega8 to detect the moment of zero crossing and then measures the time it takes to discharge in order to detect key presses.

I use analog comparator to detect the moment of zero crossing and the charge is evaluated by measuring time. Builtin AVR ADC probably wouldn’t be very useful here because the charge that can be built up is very small.

Update: [Viacheslav] left a comment to let us know we had it wrong. Instead of using the ADC, the analog comparitor is used. This change has been made above.

That would look *awesome* on some door entry keypad, which I would love to get to building some time… Hm… I have an atmega8 or two laying around, and a programmer… Just need to find me a PC with a parallel port, or a converter to parallel for programming. Harharhar!

Correction: I use analog comparator to detect the moment of zero crossing and the charge is evaluated by measuring time. Builtin AVR ADC probably wouldn’t be very useful here because the charge that can be built up is very small.

That would be very interesting as it would add a whole new layer to the process of opening the door. Someone may find the combination but they can’t open it without knowing how you press the buttons (how much pressure is applied on each one).

Of course in reality combination locks are only used in places that lots of people need to come and go from :)